Grinding wheel having an antimony or bismuth trioxide bond



United States Patent 3,317,295 GRINDING WHEEL HAVING AN ANTIMONY ORBISMUTH TRIOXIDE BOND Paul L. Kuzmick, 30 Oval Road, Essex Fells, NJ.07021 No Drawing. Filed Oct. 17, 1963, Ser. No.

317,077 16 Claims. (Cl. 51-308 The present invention relates to anabrasive element, such as a grinding wheel or the like. i

The useful life of abrasive elements such as grinding wheels is anexceedingly significant factor. All wheels wear as they are being used.The greater the wear, the shorter is the effective life of the grindingwheel. The problem of wear is particularly significant when the objectbeing machined is exceptionally resistant to abrasion; tungsten carbideparts are of this character. Industrially many grinding operations areperformed on tungsten carbide parts, but the cost of such machiningoperations is quite high because of the resistance to abrasion whichtungsten carbide exerts. This resistance reflects itself in: a low rateof carbide removal, necessistating long operating times, and in arelatively rapid rate of grinding wheel wear, resulting in the necessityfor frequent replacement of worn grinding wheels with new ones.

It is the prime object of the present invention to devise a grindingwheel which will in large measure ameliorate the problems set forth andwhich will be capable of grinding hard materials such as tungstencarbide considerably more rapidly than has heretofore been consideredpossible, and with much less wear on the grinding wheel. The magnitudeof the improvement in functioning characteristic of the grinding wheelof the present invention is made apparent when the efiiciency ratio ofthe devices of the present invention is compared with the efficiencyratio of comparable prior art devices (the efiiciency ratio is definedas the ratio between the volumetric parts of carbide removed and thevolumetric parts of the grinding wheel material which are worn away).Whereas for dry grinding of carbide an efficiency ratio of 40-50z1 hasbeen considered good, and whereas the efiiciency ratio can be raised toabout 325:1 in the case of wet grinding with a wheel having a vitrifiedbond, devices made in accordance with the present invention in a drygrinding procedure have an efficient ratio of approximately 1400: 1.

For grinding carbides and other comparable materials theabrasiveparticles employed are usually diamonds. The problem in a grinding wheelis largely to hold the diamond particles in place for an optimum periodof time and to prevent them from becoming broken or degenerated. Theexact mechanism which permits a bonded material to perform its functionis not accurately known, although many theories have been advanced. Theselection of a particular type of bonding material, or a particularcomposition or combination of compositions within a given type ofmaterial, is a more or less empirical matter.

I have found that grinding wheels having surprisingly improved drygrinding characteristics can be produced if, as a major component of thebonding material, there is employed either antimony trioxide or bismuthtrioxide or mixtures of the two. The trioxide bonding material, in theform of small granules or particles, is thoroughly mixed with theabrasive particles, preferably synthetic diamonds, and the mixture isthen compacted and sintered under pressure and temperature to form anend product in which the diamond particles are securely held by a matrixof the trioxide material. While the precise action of the trioxidebonding material in imparting to the end product the greatly improvedproperties which are characteristic thereof is not fully known, it isbelieved that the trioxide bonding material softens sufiiciently underthe heat and pressure attendant upon the grinding operation so as toactually continuously regrip the active diamond particles, holding themfirmly in place and permitting each of them to perform a maximum amountof grinding action on the tungsten carbide or other work object. It isalso thought that the trioxide bonding material may provide a certaindegree of lubricating effect between itself'and the work otlaljeclt,thereby further reducing the wear on the grinding w ee While the bondingmaterial may consist exclusively of the sintered trioxides set forthabove, it has been found in practice that the addition thereto of smallamounts of certain hard glasses will add to the strength of the finishedproduct, and in particular will effectively eliminate any tendency onthe part of the product to crumble or chip at corners or narrow sectionsthereof. The nature of the glass used is not particularly critical,provided that it falls within the category of a hard glass and that ithas a melting point within the range of that of the trioxide bondingmaterials. When the trioxide bonding material is antimony trioxide theglass used should soften at a temperature not below 1100" F. andpreferably between 1100 and 1200 F. When the trioxide used is bismuthtrioxide the glass used should soften at a temperature not below 1200F., and preferably between 12001300 F. The amount of glass used may varyrather widely. On the basis of parts by weight of trioxide bondingmaterial, a maximum of approximately 40 parts by weight of glass appearsto be indicated, with 10-30 parts representing the optimum range andwith approximately 20 parts being preferred. The glass is incorporatedinto the abrasive product initially in the form of a frit which is mixedwith the trioxide and the abrasive particles before subjecting themixture to the compacting and sintering operation.

Typical of the type of glass which can be compounded with the trioxidebond is a barium aluminum borate glass the composition of which isapproximately 20% barium oxide, 30% aluminum oxide and 50% boric acid.This glass is particularly well adapted for use in conjunction withantimony trioxide. With bismuth trioxide a glass having the followingcomposition has given very effective results:

This glass forms a tough hard frit which softens around 1300 F. and hasa low coeificient of expansion. This latter property is advantageous,since it minimizes the internal stresses set up in the wheel when it isused.

It has been found that the bond may be toughened by adding thereto, inthe original mixture, a small amount of high purity carbon particles(furnace carbon black, 99|-% pure, for example), which appears to act inthe nature of a homogenizing material. As many as 15 parts by weight ofcarbon for each 100 parts by weight of trioxide bonding material appearto be permissible. When carbon is present at these upper ranges ofconcentration a tendency toward excessive hardness on the part of thegrinding wheel has been noted. Two parts of carbon per 100 parts oftrioxide bonding material give excellent results, and it is preferedthat the carbon be present in amounts between /2-1 part per 100 parts oftrioxide. With bismuth trioxide a somewhat higher concentration ofcarbon seems to be called for than when antimony trioxide is used, inorder to produce similar end results.

If desired, a filler material may be incorporated into the abrasiveunit. Any standard filler known to be suitable for use in grindingwheels can be used, provided that its softening point is well above theforming temperatures (1100-1300 F.) for the products here disclosed.Silicon carbide, aluminum oxide, silica and cryolite are typical ofappropriate fillers. The amount of filler may be varied widely, up toapproximately 50% by weight of the total constituents of the endproduct.

While the applicability of the bonding material here disclosed is notlimited thereto, it has been found particularly effective when theabrasive particles are in the form of diamonds, and especially syntheticdiamonds. Synthetic diamond particles used for abrasive purposes have ashape and a rough surface such that they are apparently anchored inplace extremely firmly by the trioxide bond here disclosed. Naturaldiamonds have been used successfully in combination with the bond of thepresent invention, but with inferior results when compared to the use ofsynthetic diamonds. When, however, the surfaces of the natural diamondare roughened by etching before being mixed with the bonding material,the performance characteristics of the end product are greatly improved,and approach those of grinding wheels using synthetic diamonds.

While it is possible to make an entire grinding wheel from thecomposition here disclosed, it is usually uneconomical to do so, andexcellent results can be achieved by forming the abrasive composition ofthe present invention as a rim on a preformed core. The nature of thecore may be widely varied. I have found that a standard vitrifiedgrinding wheel functions quite well in that regard, since it is strongenough to withstand the forming temperatures and pressures to which theabrasive composition of the present invention is subjected. A vitrifiedcore comprising one part by weight of a glass which melts atapproximately 1800 F. and five parts by weight of aluminum oxide alsoproduces a desirable core. In general, any material of suitablestructural strength which will not soften when subjected to theformation temperatures and pressures of the composition of the presentinvention will be satisfactory.

A typical formulation for the bonding material is as follows:

Example I Parts by weight Antimony trioxide (230 mesh) 100 Bariumaluminum borate glass (230 mesh) 20 Carbon /2 1000 mesh silicon carbide(filler) 30 A'second typical formulation is as follows:

Example 11 Parts by weight Bismuth trioxide (-230 mesh) 100 Glass frit(230 mesh) 15 1000 mesh silica carbide (filler) 20 Pure carbon l Theabove ingredients are ball-milled for a period of 24 hours in order toensure that all of the ingredients are thoroughly mixed. Thereafter theabrasive particles are mixed therewith. The amount of diamond particlescan be varied widely, and as many as 80 carats of diamonds per cubicinch of wheel can be used. The normal commercial concentrations, whichusually range between 18 and 72 carats of diamond per cubic inch ofwheel, are also appropriate. The bonding material here disclosed iscapable of carrying both high and low diamond concentrations, ranging,for purposes of exemplification and not limitation, from 18 carats percubic inch to 144 carats per cubic inch.

The mixture of bonding material and abrasive particles is then placed inan appropriate mold, preferably of the high density graphite type,together with the supporting core if such a core is used. By way ofspecific example, in order to produce a grinding wheel having a 5" outerdiameter a core having an outer diameter of 4.875 inches may be used.The radially outer surface of that core may be pretreated in knownfashion for better adhesion to the rim of abrasive material to be formedthereon. The mold, in such a case, has an internal diameter ofapproximately 5 inches, and the space between the mold and the core isfilled with the mixture of bonding material and abrasive particles.

In filling the space between the mold and the 4.875 inches diameter corein order to produce a 5" diamond grinding wheel, the followingproportions of bonding material and abrasive particles are exemplary:

Example IV When the bonding material comprises bismuth trioxide insteadof antimony trioxide the proportions are the same as in Example I,except that the trioxide bonding material is present in the amount ofcarats.

After the mold has been filled, it is closed and then subjected to thesimultaneous action of heat and pressure. The pressure may be exerted bya hydraulic press, to approximately 1500 psi. Heat may be applied in anyap propriate manner, as through the use of induction coils 0relectrically heated platens. The temperature is raised to 1100 F. whenantimony trioxide alone is involved or to 1200 F. when bismuth trioxideis used. These molding temperatures should, for best results, be held towithin a few percent, and preferably 1-2%, of the values specified. Theheat and pressure is continued for approximately 15 minutes, after whichthe heat is removed and the mold and its contents are permitted to coolapproximately 300 F. before the pressure is released. Thereafter themold is permitted to cool in air and the finished product is removedtherefrom.

The vastly improved abrasive action of the devices here disclosed, whencompared with the prior art, may be seen from the following testresults. 5" x A diamond wheel having a diamond abrasive rim portionformed in accordance with the present invention was rotated at 2700 rpm.in a commercial grinding machine having a downfeed of .001 inch perpass, a cross feed of .042 inch per pass, and a table speed of 50 feetper minute. The work object was a 6" x 3" piece of No, 44A tungstencarbide. The total downfeed (a measure of the depth of carbide removed)was .100 inch. The total wheel wear could not even be measured by amicrometer, so small was it, and highly accurate measuring techniquesindiiated that the radius of the wheel decreased only .000325 inch. Thismade for an efficiency ratio of 1392.6: 1. This is to be compared withefficiency ratios of 40-5021 for dry grinding of tungsten carbide withresinoid bonded diamond wheels, and it is even many times greater thanthe efliciency ratios of 200:1 and 325:1 which are considered good forwet grinding of tungsten carbide with prior art resin bonded andvitrified bonded diamond wheels. It may be noted that with thecomposition here disclosed the finish produced on the tungsten carbidework object was better than normal, and no overheating occurred.

A 4" cup-type wheel having an abrasive area made in accordance with thisdisclosure was, in a dry grinding procedure, rotated at 3600 r.-p.m.,with a downfeed of .001 inch per pass and a traverse of 250 inches perminute. The workpiece was a /2 x piece of No. 44A tungsten carbide. Thetotal downfeed was .250 inch. The wheel wear, measured along the radiusof the wheel, was only .000275 inch. This made for an efficiency ratioof 409.6:1. This is to be compared with an efiiciency ratio of 20-30:1for prior art resinoid bonded cup-type wheels in a dry grindingprocedure.

The grinding wheel of the present invention does not appear to besuitable for wet grinding, except under very carefully controlledconditions, since a tendency has been noted for the diamond particles toloosen and separate from the abrasive wheel during wet grinding. It isbelieved that the bonding material is affected by the Water, and perhapsis slightly soluble therein.

However, for dry grinding, and particularly dry grinding of hardmaterials such as tungsten carbide, abrasive wheels made in accordancewith this disclosure give results vastly superior to the best that theprior art has been able to show, particularly insofar as wheel wear isconcerned. When it is considered that, in industrial operationsperformed on tungsten carbide parts, grinding wheels wear out rapidlyand therefore must be changed frequently, it will be appreciated thatthe expense of the wheels themselves and the down time of the machinesWhile the wheels are being replaced are both very significant costfactors. Use of grinding wheels made in accordance with the presentinvention will, because of their much greater life when compared withthe best that the prior art has to offer, result in a very significantsaving without any decrease in accuracy or in machine speed, and with asensible increase in the quality of the finish produced on the tungstencarbide piece.

While but a limited number of embodiments of the present invention havebeen here specifically disclosed, it will be apparent that manyvariations may be made therein, all within the scope of the followingclaims.

Iclaim:

1. A grinding wheel comprising diamond abrasive particles and consistingessentially of a sintered composition selected from the group consistingof antimony trioxide, bismuth trioxide, and mixtures thereof.

2. A grinding wheel comprising diamond abrasive particles and a bend amajor proportion of which consists essentially of a sintered compositionselected from the group consisting of antimony trioxide, bismuthtrioxide, and mixtures thereof and a minor proportion of which consistsessentially of a hard glass having a softening temperature aroundl100-1200 F. or IZOD-1300 F. when used with antimony trioxide or bismuthtrioxide respectively.

3. The grinding wheel of claim 2, in which said trioxide is present inproportions of 100 parts by weight and said glass is present inproportions up to 40 parts by weight.

4. The grinding wheel of claim 3, in which said bonding compositioncomprises a small amount, less than parts by weight for 100 parts byweight of said trioxide, of particles of high purity carbon.

5. The grin-ding wheel of claim 3, in which said bonding compositioncomprises particles of high purity carbon in proportions of .5-1 part byweight for 100 parts by weight of said trioxide.

6. The grinding wheel of claim 3, in which said bonding compositioncomprises a filler material having a softening point above around 1200F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively.

7. The grinding wheel of claim 3, in which said bonding compositioncomprises a filler material having a softening point above around 1200F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in an amount up to 50parts by weight of each 100 parts by weight of trioxide.

8. The grinding wheel of claim 3, in which said bonding compositioncomprises a filler material having a softening point above around 1200"F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in an amount between20-30 parts by weight for each parts by weight of trioxide.

9. The grinding wheel of claim 3, in which said bonding compositioncomprises particles of high purity carbon in proportions between .5-1part by weight for 100 parts by weight of said trioxide, and furthercomprises a filler material having a softening point above around 1200F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in amounts between20-30 parts by weight for each 100 parts by weight of trioxide.

1-0. The grinding wheel of claimZ, in which said bonding compositioncomprises particles of high purity carbon in proportions of .5-1 part byweight for 100 parts by weight of said trioxide.

11. The grinding wheel of claim 2, in which said bonding compositioncomprises a filler material having a softening point above around 1200"F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in an amount between20-30 parts by weight for each 100 parts by Weight of trioxide.

12. The grinding wheel of claim 2, in which said bonding compositioncomprises particles of high purity carbon in proportions between .5-1part by weight for 100 parts by weight of said trioxide, and furthercomprises a filler material having a softening point above around 1200F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in amounts between20-30 parts by weight for each 100 parts by weight of trioxide.

13. The grinding wheel of claim 2, in which said trioxide is present inproportions of 100 parts by Weight and said glass is present inproportions of 1030 parts by weight.

14. The grinding wheel of claim 13, in which said bonding compositioncomprises particles of high purity carbon in proportions of .5-1 part byweight for 100 parts by weight of said trioxide.

15. The grinding wheel of claim 13, in which said bonding compositioncomprises a filler material having a softening point above around 1200F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in an amount between20-30 parts by weight for each 100 parts by weight of trioxide.

16. The grinding wheel of claim 13, in which said bonding compositioncomprises particles of high purity carbon in proportions between .5-1part by weight for 100 parts by weight of said trioxide, and furthercomprises a filler material having a softening point above around 1200F. or 1300 F. when used with antimony trioxide or bismuth trioxiderespectively, said filler material being present in amounts between20-30 parts by weight for each 100 parts by weight of trioxide.

References Cited by the Examiner UNITED STATES PATENTS 2,137,201 11/1938Boyer 5l-309 2,258,774 10/ 1941 K-uzmick 5 l3 09 2,334,266 11/ 1943Houchins 51-308 ALEXANDER H. BRODMERKEL, Primary Examiner D. J. ARNOLD,Assistant Examiner.

1. A GRINDING WHEEL COMPRISING DIAMOND ABRASIVE PARTICLES AND CONSISTINGESSENTIALLY OF A SINTERED COMPOSITION SELECTED FROM THE GROUP CONSISTINGOF ANTIMONY TRIOXIDE, BISMUTH TRIOXIDE, AND MIXTURES THEREOF.
 2. AGRINDING WHEEL COMPRISING DIAMOND ABRASIVE PARTICLES AND A BOND A MAJORPROPORTION OFWHICH CONSISTS ESSENTIALLY OF A SINTERED COMPOSITIONSELECTED FROM THE GROUP CONSISTING OF ANTIMONY TRIOXIDE, BISMUTHTRIOXIDE, AND MIXTURES THEREOF AND A MINOR PROPORTION OF WHICH CONSISTSESSENTIALLY OF A HARD GLASS HAVING A SOFTENING TEMPERATURE AROUND1100-1200*F. OR 1200-1300*F. WHEN USED WITH ANTIMONY TRIOXIDE OR BISMUTHTRIOXIDE RESPECTIVELY.